A review of undulated sediment features on Mediterranean prodeltas: distinguishing sediment transport structures from sediment deformation

Most Mediterranean prodeltas show undulated sediment features on the foresets of their Holocene wedges. These features have been described all along the Mediterranean for the last 30 years and interpreted as either soft sediment deformation and incipient landsliding, and more recently, as sediment transport structures. We perform a review and detailed analysis of these undulated sediment features using ultrahigh-resolution seismic and bathymetric data as well as geotechnical information and hydrodynamic time series and hydrographic transects. In this study we show that the characteristics of the sediment undulations (configuration of the reflections down section and between adjacent undulations and overall morphologic characteristics) are incompatible with a genesis by sediment deformation alone and do not show evidence of sediment deformation in most cases. Various processes in the benthic boundary layer can be invoked to explain the variety of features observed in the numerous areas displaying sediment undulations.     

Quaternary stratal architecture of the Barcelona prodeltaic continental shelf (NW Mediterranean)

The Barcelona continental shelf is part of a 6–20 km wide canyon-bounded shelf located off the city of Barcelona (NE Spain). This study integrates newly acquired high-resolution single channel seismic reflection profiles and available lithological information of the Barcelona shelf to describe its late Quaternary architecture and the role of global glacio-eustatic fluctuations and local factors in its development.

Four major sequence boundaries are identified throughout the seismic dataset. They are tentatively correlated with the four last 4th order (100–120 ka) high-amplitude late Quaternary glacio-eustatic lowstands. Most of the stratigraphic record is formed by falling stage systems tracts with forced-regressive deposits, which confers a general progradational vertical stacking pattern. Transgressive systems tracts are represented by continuous units confined directly off river sources and on previously eroded surfaces. Stillstand deposits are difficult to recognize in the available dataset. The uppermost seismic unit corresponds to the Holocene shore-parallel Besos and Llobregat joint prodelta affected by the prevailing south-westward circulation.

The general architecture of the late Quaternary Barcelona shelf deposits is determined by global glacio-eustatic cycles. However, the lateral variability of the seismic units depends largely on local factors such as (i) the position of sediment sources (essentially the Llobregat River); (ii) differential subsidence and, especially, sediment compaction; (iii) erosive processes such as canyon incision, mass wasting or wave base dynamics; and (iv) underlying geomorphic restrictions.     

Plant macrofossil assemblages from surface sediment represent contemporary species and growth forms of aquatic vegetation in a shallow Mediterranean lake

Macrofossils are known as a useful tool in reconstructing their original plant communities. However, most studies have been focused on comparing the composition and distribution of living plant communities and their remains in temperate lakes. Mediterranean shallow lakes have been historically far less studied and little is known about the relationships between Mediterranean macrophyte communities and their remains. The aim of our study is to assess how contemporary aquatic macrophyte communities are represented by their sedimentary remains in terms of composition, distribution and concordance between the contemporary and the subfossil assemblages in a procrustean superimposition space, and to determine which surface sediment cores, collected along a depth gradient, may represent best the whole-lake macrofossil assemblage. These analyses were carried out for both species and macrophyte growth forms (submerged hydrophytes, floating-leaved hydrophytes, helophytes and charophytes) in order to check which of the two (species and growth forms) were represented best by their macro-remains. The most abundant present-day species (Myriophyllum alterniflorum DC. and Potamogeton trichoides L.) were under-represented while Characeae and some floating-leaved hydrophytes (Polygonum amphibium L. and Ranunculus peltatus Schrank) were over-represented in sedimentary samples. Additionally, macro-remains of submerged hydrophytes and helophytes were generally found in the central areas and in close proximity to contemporary vegetation, whereas floating-leaved hydrophytes distributed close to the near-shore. Notwithstanding some disparities between contemporary vegetation and their macrofossil assemblages, we found a good agreement between present-day and sedimentary datasets for both species and macrophyte growth forms. Furthermore, our study suggests that sediment cores from deep areas are more likely to represent best the whole-lake macrofossil assemblage because of their high diversity, equitability and heterogeneity. We conclude that aquatic macrophyte subfossils from the central areas of the basin can be a very useful tool in tracking the species composition and structure of the original macrophyte communities in shallow Mediterranean lakes. Additionally, when considering the use of macro-remains to reconstruct the composition and structure of macrophyte growth forms, we recommend a multicore approach that uses transects running from the shore to the lake center.     

Long-term development and current status of the Barcelona continental shelf: A source-to-sink approach

The Barcelona continental shelf, off the city of Barcelona (NE Spain), is a relatively narrow canyon-bounded shelf in the northwestern Mediterranean Sea. Three medium-size rivers (Tordera, Besós and Llobregat) and several ephemeral rivulets flow into this margin. Two main domains have been recognized in the Barcelona shelf: (i) a modern, river-influenced area, and (ii) a relict, sediment depleted area, both affected by a variety of human impacts. A detailed geomorphologic study based on multibeam bathymetry and backscatter data, high resolution seismic profiles, and surface sediment samples allowed mapping and interpreting the main distinctive seafloor features on the Barcelona shelf. Modern sedimentary features reveal that the Llobregat River is the main sediment source of the Barcelona prodeltaic shelf. High-discharge fluvial events result in the formation of suspended sediment plumes and sediment waves on the shelf floor. Relict (late Pleistocene–Holocene) sedimentary features reflect that an important shift occurred in the seashore direction between MIS 4 and MIS 2, and that recent neotectonic reactivation has created a set of seafloor faults. The Barcelona inner and middle shelf is severely impacted by anthropogenic activities such as the enlargement works of the Port of Barcelona, sewage pipes, dredging, anchoring and trawling.     

Ecological assessment of highly heterogeneous systems: The importance of taxonomic sufficiency

We assess the effects of taxonomic resolution (genus-family levels) on the ecological assessment of 39 highly heterogeneous ponds located in north-western Spain.Non-metric multidimensional scaling (MDS) and one-way analysis of similarities (ANOSIM) were used to investigate the effects of taxonomic resolution on the macroinvertebrate assemblage structure. The Mann Whitney U-test and discrimination efficiency were used to assess the ability of nine diversity measures (total richness, rarefied richness samples of 25, 50 and 100 individuals, Margalef's index, Pielou's evenness, Shannon-Weaver's index, Simpson's index and percent dominant taxon) to discriminate between acceptable (best available and good conditions) and unacceptable (moderate, poor and very poor) conditions using three levels of taxonomic resolution: (i) family, (ii) family plus subfamilies of benthic non-biting midges and (iii) genus level.Based on non-metric MDS, the macroinvertebrate assemblages of ponds of acceptable (A) and unacceptable (N) conditions were statistically undistinguishable, both at genus and family levels. On the other hand, based on several community metrics (total richness, Margalef index, etc.) the two sets of samples were statistically different, although only when the genus or the subfamily level was used and after Bonferroni correction. These results suggest that the structure of macroinvertebrate assemblages by itself is more sensitive than the specific composition in distinguishing the fauna living in acceptable and unacceptable conditions. Moreover, dealing with families including many taxa generally showing different tolerance to disturbance may lead to misclassification of ponds. We agree, however, that the two approaches, i.e. assemblage composition and diversity measures, are conceptually different and hence they should be used in combination for a better understanding of the response of single metrics.     

SMART-1 mission description and development status

SMART-1 is the first of the Small Missions for Advanced Research in Technology of the ESA Horizons 2000 scientific programme. The SMART-1 mission is dedicated to testing of new technologies for future cornerstone missions, using Solar-Electric Primary Propulsion (SEPP) in Deep Space. The chosen mission planetary target is the Moon. The target orbit will be polar with the pericentre close to the South-Pole. The pericentre altitude lies between 300 and 2000 km, while the apocentre will extend to about 10,000 km. During the cruise phase, before reaching the Moon, the spacecraft thrusting profile allows extended periods for cruise science. The SMART-1 spacecraft will be launched in the spring of 2003 as an auxiliary passenger on an Ariane 5 and placed into a Geostationary Transfer Orbit (GTO). The expected launch mass is about 370 kg, including 19 kg of payload. The selected type of SEPP is a Hall-effect thruster called PPS-1350. The thruster is used to spiral out of the GTO and for all orbit maneuvers including lunar capture and descent. The trajectory has been optimised by inserting coast arcs and the presence of the Moon's gravitational field is exploited in multiple weak gravity assists.The Development Phase started in October 1999 and is expected to be concluded by a Flight Acceptance Review in January 2003. The short development time for this high technology spacecraft requires a concerted effort by industry, science institutes and ESA centres. This paper describes the mission and the project development status both from a technical and programmatic standpoint.